Method of making hexaorganodiplumbanes

ABSTRACT

Method of making hexaorganodiplumbanes, Pb2R6, by reacting a lead carboxylate and an organoaluminum compound, AlR3, where R is aliphatic or cycloaliphatic.

United States Patent Buschhoff 5] June 20, 1972 [54] METHOD OF MAKING 2,955,124 10/1960 Blitzer et al ..260/437 R HEXAORGANODIPLUMBANES OTHER PUBLICATIONS [72] lnventor: Max Buschhofi, Luenen, Germany Chemical Abstracts, VOL 55 153358 (1961) [73] Assignee: Schering AG, Berlin, Germany Chemical Abstracts, 541973880960) Calingaert, J. Org. Chem. 2,535 (1938)(QD- 241-16) [22] Med: 1969 Pearson et aL, Adv. in Chemistry Series, No. 23, Amer. Chem 211 App] No: 9 70 506., Wash, D.C., pp. 302- 303 (1959) (OD- 411- A5) Primary E.\'aminer-Tobias E. Levow [30] Foreign Application Pr ority Data Assistant Examiner-H. M. S. Sneed Jan. 7, 1969 Germany ..1 19 01 030.1 Sam"! 52 us. (:1 ..260/437 R, 260/448 A [57] ABSTRACT [51] Int. Cl. ..C07f 7/24 Method of making hexaorganodiplumbanes, Pb R by react- [58] Field of Search ..260/437 ing a lead carboxylate and an organoaluminum compound,

AlR where R is aliphatic or cycloaliphatic. [56] References Cited 7 Claims, No Drawings UNITED STATES PATENTS 2,859,231 11/1958 Blitzer et a1 ..260/437 R METHOD OF MAKING HEXAORGANODIPLUMBANES METHOD OF MAKING HEXAORGANODIPLUMBANES The present invention relates to methods of making hexaorganodiplumbanes.

Hexaorganodiplumbanes are organo-metallic compounds which, inter alia, are useful as precursors in the preparation of trialkyl lead salts. Such conversion reactions are taught, for example, in Organolead Chemistry" by L. C. Willemsens, page 66, International Lead-Zinc Research Organization, 292 Madison Avenue, New York, New York 10017, (February 1964) and in The Organic Compounds of Lead" by H. Shapiro and F. W. Frey, page 4l6 et seq., John Wiley & Sons, New York I968).

It is known in the art to prepare organo lead compounds by the alkylation of lead salts (cf. L. C. Willemsens, op. cit.) Other metal alkyls are usually used as alkylating agents, especially those of metals of Groups I [ll of the Periodic System. As lead salts, lead acylates (Pb ll and Pb IV), as well as lead oxide and lead sulfide are used, in addition to the lead halides. In all these reactions, tetraalkyl lead compounds are obtained irrespective of the lead salt and alkylating agent employed. Thus, the reaction of lead chloride with Grignard reagents takes place according to the following reaction scheme:

It is possible to isolate hexaorganodiplumban es in solution only if alkyl compounds of metals of Groups I and II of the Periodic System are used for alkylation, in particular lithium and magnesiumalkyls, and only when the reaction is carried out under carefully controlled conditions. Although this may be suitable in the laboratory, its use on a technical scale is unfeasibly difficult.

For large scale reactions, the easily obtainable alkyl compounds of metals of Group III of the Periodic System, which compounds are easy for the skilled chemist to handle, are particularly useful. But processes for making hexaorganodiplumbanes from lead salts and metal alkyls of this type have heretofore not been known. In such reactions, tetraalkyl lead compounds have always been obtained (cf. L. C. Willemsens, op. cit., and German Pat. No. 1,216,301).

According to the present invention, hexaorganodiplumbanes are prepared by reacting lead (II) or lead (IV) salts of organic acids, particularly salts of lower alkanoic acids such as the acetates, with compounds of aluminum of the general formula AIR wherein R is aliphatic or cycloaliphatic, suitably a saturated or olefinically unsaturated aliphatic hydrocarbon having up to about carbon atoms in a chain which may be straight or branched, or a cycloaliphatic hydrocarbon.

The lead salts employed are of the type Pb(OCOR) or Pb(OCOR),, wherein R is an aryl radical or a saturated or unsaturated aliphatic or cycloaliphatic radical, suitably a hydrocarbon radical. Salts of lower alkanoic acids (e.g. C C acids) are particularly preferred.

The lead salts are combined with the aluminum compounds, preferably while the latter are in solution. As solvents, toluene is preferably employed, but other aromatic and aliphatic hydrocarbons and chlorinated hydrocarbons can be used, as well as straight-chain and branched chain aliphatic, cyclic, and aromatic ethers, if they are inert, i.e. if they do not react with the alkylating agent. Suitable solvents include but are not limited to benzene, xylene, heptane, anisol, and methylene chloride.

The reaction temperature may be between about 70 C. and +40C., but is preferably between about -5 C. and +5 C.

The reaction of the present invention is believed to take place according to the following scheme:

armooon n GAlR; aPbm GAIRKOCOR) arbm Pbna, Pb

To isolate the hexaorganolead compound from the reaction mixture, the dialkylaluminum acylate formed is suitably converted into a product insoluble in the organic solvent phase. For example, the acylate can be decomposed by adding water, preferably ice-water, to precipitate aluminum hydroxide which is then physically separated from the organic phase by techniques such as filtration or centrifugation. Alternatively, the amphoteric precipitate which would otherwise form can be converted to water-soluble species by treatment with an acid or base at a pH outside the range of 3.5 to 13. Still further, the aluminum can be reacted with a complexing agent such as sodium potassium tartrate or sodium oxalate to form a water-soluble complex.

In a preferred embodiment, the reaction is carried out by adding an anhydrous lead acylate in a mol ratio of 1:2 to a solution of the aluminum compound in an inert organic solvent under a dry protective atmosphere such as of nitrogen or one of the rare gases. After addition is complete, it is advantageous to let the materials react for l 2 hours at 40 C. Thereafter, the reaction mixture is added to a mixture of ice, concentrated hydrochloric acid and water to decompose the dialkylaluminum acylate and the content of hexaorganodiplumbane in the organic phase is determined iodometrically.

A better understanding of the present invention and of its many advantages will be had by referring to the following specific Examples given by way of illustration.

EXAMPLE l 163 g. (0.5 mol) of finely-powdered anhydrous lead (II) acetate were added with stirring at 5 C. to a solution of 198 g (1 mol) of aluminum tributyl in 500 ml. of toluene. After addition was complete, the mixture was heated for 1 hour at 40 C. The reaction mixture was then carefully added to a mixture of 200 ml. concentrated hydrochloric acid, 200 ml. of water, and 500 g of ice to decompose the dibutylaluminum acetate formed by the reaction. The yellow toluene phase was separated and its content of hexabutyldiplumbane was determined iodometrically. The yield, calculated on the amount of lead acetate employed, was percent.

Alternatively, aluminum hydroxide can be precipitated by the addition of ice and water alone, and then removed by filtration or centrifugation. Aqueous solutions of a base, such as sodium hydroxide or potassium hydroxide, at a pH greater than 13 can also be used to separate the desired hexabutyldiplumbane from aluminum compounds present in the reaction mixture.

Although the hexaorganodiplumbane products can be isolated by evaporation of the solvent, they are conveniently left in solution in the organic solvent phase.

EXAMPLES 2 8 In each Example, mol of organoaluminum compound was EXAMPLES 9 11 In each Example, 198 g (1 mol) of aluminum tributyl were reacted with 163 g (0.5 mol) of anhydrous lead (ll) acetate as in Example I using 500 ml. of different inert solvents.

Example No. Solvent Yield 9 Benzene 50 10 Anisol 60 l l Methylene Chloride 60 EXAMPLES 12 13 198 g (1 mol) of aluminum tributyl were reacted in each case with 0.5 mol of an anhydrous lead (ll) acylate in 500 ml. of toluene, as in Example 1.

2 e wherein R is aliphatic hydrocarbon or cycloaliphatic hydrocarbon, which method comprises adding one molar part of a lead (ll) carboxylate to two molar parts of an aluminum compound of the formula AIRS 9 where R has its earlier meaning, at a temperature from about C. to about 40 C.

2. The method as in claim 1 wherein said lead carboxylate and aluminum compound are reacted at a temperature from about 5 C. to +5 C.

3. The method as in claim 1 wherein said lead carboxylate is a lead (ll) compound.

4. The method as in claim 1 wherein said lead carboxylate is a salt of a lower alkanoic acid.

5. The method as in claim 1 wherein said lead carboxylate and aluminum compound are reacted in an organic solvent inert to the reaction.

6. The method as in claim 5 wherein said inert solvent is an aliphatic or aromatic hydrocarbon or chlorinated hydrocarban or an ether.

7. The method as in claim 1 wherein the hexaorganodiplumbane reaction product is isolated by converting aluminum compounds formed by the reaction into compounds insoluble in an organic solvent phase. 

2. The method as in claim 1 wherein said lead carboxylate and aluminum compound are reacted at a temperature from about -5* C. to +5* C.
 3. The method as in claim 1 wherein said lead carboxylate is a lead (II) compound.
 4. The method as in claim 1 wherein said lead carboxylate is a salt of a lower alkanoic acid.
 5. The method as in claim 1 wherein said lead carboxylate and aluminum compound are reacted in an organic solvent inert to the reaction.
 6. The method as in claim 5 wherein said inert solvent is an aliphatic or aromatic hydrocarbon or chlorinated hydrocarbon or an ether.
 7. The method as in claim 1 wherein the hexaorganodiplumbane reaction product is isolated by converting aluminum compounds formed by the reaction into compounds insoluble in an organic solvent phase. 